Nutrition in Animals


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In today’s class, we will be talking about nutrition in animals. Enjoy the class!

Nutrition in Animals

Nutrition in Animals

All living organisms need food for their survival and daily activities. Plants can manufacture their food through a process called photosynthesis, hence they are called autotrophs. On the other hand, animals cannot manufacture their own food as they depend on plants directly or indirectly for their food, hence they are called heterotrophs.

Animals sometimes are classified according to the type of food they eat. On this basis, they are classified into three groups, namely:

  1. Carnivorous animals: These animals feed only on flesh or other animals, e.g dog, lion, lizard, snake, cat, etc.
  2. Herbivorous animals: These animals feed on plants, e.g. goat, sheep, rabbit, etc.
  3. Omnivorous animals: These animals feed on both plants and animals, e.g. man, pig, etc.

Classes and sources of food

There are seven major classes of nutrients :

  • Carbohydrates
  • Fats
  • Fibre
  • Minerals
  • Protein
  • Vitamin
  • Water.
Importance of carbohydrates
  1. They provide us with energy.
  2. It provides heat during its oxidation which is used in maintaining body temperature.
  3. It is used in building the exoskeleton of arthropods.
Importance of proteins
  1. Protein is needed for bodybuilding
  2. They are necessary for building new cells and replacing old ones.
  3. Essential for the repair of cells and worn- out tissues.
  4. They are essential for the formation of enzymes
  5. Essential for the formation of hormones.
Importance of fats and oils
  1. Fats and oil are used for energy storage in the body.
  2. They provide more energy to the body than carbohydrate when metabolized.
  3. They are solvents for fat-soluble vitamins and also for hormones.
  4. They are important components of cell membranes.
  5. They help in maintaining body temperature.
 Mineral Salts:

Mineral salts regulate the metabolic activities within the body. They are also important in the formation of enzymes, pigments and structural parts of living organisms.

The major source of mineral salts is the food we eat. Examples of minerals include sodium, potassium, calcium, chlorine, phosphorus, magnesium, iron, copper, cobalt, fluorine and manganese.

lack of minerals in our diet results to ill health and development of symptoms of deficiency diseases.


Vitamins are organic compounds required by humans and other animals in only small quantities for normal growth and healthy development. They promote chemical reactions in the body.

Examples include vitamins A, D, E and K, etc. Inadequacy or lack of these vitamins leads to nutritional deficiency diseases and ill health.


Water is very important in our diet. Sources of water include metabolic water in the food we eat and water is taken in.

Importance of water
  • It is required for metabolic activities in the body.
  • It transports digested food substances, excretory products and hormones.
  • It helps in the regulation of body temperature.
  • It helps to maintain the osmotic content of the body tissues.
  • It plays an important role in digestion.
  • It constitutes a greater part of the blood.
  • It is the main component of plants and animals.

Balanced diet

A balanced diet is a diet containing the correct proportion or the right amount of all the six food substances required by an organism or man. The balanced diet must contain the six food substances such as carbohydrates, proteins, fats and oil, minerals, vitamins and water.

Importance of a balanced diet

A balanced diet is important to the body in the following ways:

  • A balanced diet makes us healthy and by so doing, makes us be resistant to diseases.
  • It encourages growth and normal development of the body.
  • It also provides the energy required for normal activities.
  • Balanced diet prevents malnutrition, deficiency or diseases. Lack of some food substances, e.g protein in a diet can cause a nutritional disease called kwashiorkor in children.

Digestive enzymes

An enzyme is an organic catalyst usually proteinous in nature, which promotes or speeds up chemical changes in living cells but are not themselves used up in the process.

Enzymes accelerate metabolic reactions without changing their composition in the process.

Characteristics of enzymes
  • They are protein in nature;
  • They remain chemically unchanged at the end of a reaction;
  • They are specific in action
  • Enzymes are required in small quantities;
  • They act over a specific range of temperature
  • They are destroyed at high temperature
  • They act best at a specific pH
  • most actions are reversible;
  • enzyme action is retarded by poison or inhibitors;
  • some are inactive and require a coenzyme/agents to activate them;
  • enzymes are soluble;
  • They can function outside the body of the organism that produces them;
  • They speed up the rate of biochemical reactions in cells

A practical guide on food tests

The materials/nutrients present in food can be identified using various types of tests. These are:

  1. Test for carbohydrates:

(a) To test for simple sugar e.g. glucose and fructose.

  • Put a small quantity of glucose solution in a test tube.
  • Add an equal amount of benedict solution.
  • Boil the mixture for 4 – 6 minutes. A bricks-red or orange precipitate indicates the presence of glucose.

(b) To test for complex sugar e.g. sucrose, maltose or lactose

  • Put a small quantity of the sucrose solution in a test-tube
  • Add a few drops of dilute hydrochloric acid to the solution, (This hydrolyses the complex sugar to simple sugar)
  • Place the test-tube in a boiling water bath for a few minutes.
  • Add a few drops of dilute caustic soda (to neutralize the excess acid).
  • Add an equal amount of Fehling’s solution and place the test-tube in a boiling bath. An orange-red precipitate/yellow precipitate indicates the presence of sucrose.

(c) To test for starch

  • Boil a sample of the starch material (e.g. yam/rice)
  • Add a few drops of dilute iodine solution to it. A blue-black colouration indicates the presence of starch.
  1. To test for proteins:

(a) Biuret test

  • Take a small quantity of fresh milk, egg white solution or malt extract in a test-tube.
  • Add a few drops of water and 1cm³ of dilute sodium hydroxide.
  • Carefully add 1% of copper II sulphate solution in drops. Shake the mixture thoroughly after each drop.
  • A violet or purple, colour indicates the presence of protein
  • A pink colour indicates the presence of peptones.

(b) Millon’s test

  • Put 3cm³ of egg white or colloidal solution of a protein into a test-tube
  • Add 3cm³ of Millon’s reagent and warm the mixture in a water bath for a few minutes.
  • A deep red colour or precipitate shows the presence of protein.

(c) Xanthoproteic test

  • Put 2cm³ of egg white or milk solution in a test-tube.
  • Carefully add about 1cm³ concentrated trioxonitrate(v) acids. A white precipitate forms which turn yellow on heating.
  • Cool the contents and add about 3cm³ of ammonium hydroxide solution. Heat the solution and allow it to cool. The colour of the precipitate deepens to orange indicating the presence of protein.
  1. To test for fats and oils:

(a) Translucent mark test

  • Drop oil on a spot, on a piece of paper or rub the surface of a fatty food against the surface of a piece of white paper. A translucent mark shows the presence of fat.

(b) Sudan III test

  • Add a few drops of Sudan (iii) solution to some oil in a test-tube. The red colouration is obtained
  • Boil the solution. A black precipitate is formed.


In our next class, we will be talking about Modes of Nutrition.  We hope you enjoyed the class.

Should you have any further question, feel free to ask in the comment section below and trust us to respond as soon as possible.

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